A catalyst is used in an electric cell such as a polymer electrolyte fuel cell (PEFC), and specifically, a cathode or an anode having a layer containing a catalyst are used in order to enhance the reaction rate of a PEFC and enhance the energy conversion efficiency of a PEFC.
As this catalyst, a noble metal catalyst is generally used, and platinum, which is highly active among the noble metals, is mainly used. However, platinum is expensive, and therefore utilization of PEFCs is limited in terms of, for example, costs.
In addition, the cathode of a PEFC is in an oxidizing and strongly acidic atmosphere and has high electric potential, and therefore materials which are stable in a PEFC operating environment are extremely limited. It is known that even platinum, which is particularly stable among the noble metals, undergoes oxidation and dissolution due to long-term usage and the activity is deteriorated.
A large amount of a noble metal catalyst is used in a cathode in order to solve this problem and also from the viewpoint of keeping the power generation performance of a PEFC; however, such use of a large amount of the noble metal catalyst is a big problem in terms of both costs and resources.
A non-platinum catalyst having high catalytic activity and having high durability in an PEFC operating environment have been desired in order to solve the above-described problem, specifically, from the viewpoints such as reducing the costs and expanding the use of a PEFC.
A metal sulfide as a non-platinum catalyst has a small band gap, exhibits electrical conductivity comparable to a metal, and therefore is used as a photocatalyst or an electrode catalyst for oxidation-reduction reaction.
For example, it is described in Patent Literature 1 that a RuMoS/C catalyst can exhibit properties as a catalyst because a sulfur component is harder to eliminate in the RuMoS/C catalyst than in RuS/C. However, Ru is the main component of metal components in the RuMoS/C catalyst and therefore is not preferable in terms of costs. In addition, it is not described that CoS2 having a cubic crystal structure is substituted with a substitutional atom to improve the durability.
Searches for a material from computational chemistry approaches have been recently conducted from the viewpoints such as making experiments efficient accompanying drastic improvements in the computer performance (for example, Non Patent Literatures 1 to 3).